The present invention relates in general to integrated circuit (IC) packaging. More particularly, the invention provides an IC package with transparent encapsulant and a method for making thereof. Merely by way of example, the invention is described as it applies to a package in compliance with certain JEDEC standard, but it should be recognized that the invention has a broader range of applicability.
Integrated circuits are usually packaged before being used in electronic systems. Integrated circuit (IC) packages often protect the integrated circuits from the surrounding environment but also provide electrical connections to other components of the electronic systems. For example, the IC packages include a plurality of leads that are connected to the integrated circuits, and such leads can transmit or receive electrical signals from other components of the electronic systems. In another example, the IC packages also include encapsulant materials that cover and protect at least parts of the integrated circuits and/or the electrical connections between the integrated circuits and the leads.
For certain applications, the integrated circuits include optical sensors, which are used in light sensitive or light activated devices such as laser diodes. To meet this demand, IC packages with transparent windows have been developed. FIG. 1 is a conventional IC package with a transparent window. The IC package 1 can be used as a ceramic dual-in-line package (CERDIP) of a charge-coupled device (CCD). As shown in FIG. 1, the package 1 includes a die 11, a ceramic lower plate 12, a leadframe 14, a ceramic upper plate 15 and a window 10. The lower plate 12 serves as a die pad. The die 11 includes an integrated circuit coupled to a light sensor 19.
Additionally, a die sealant 13 is applied to one side of a central portion of the die pad 12, and the die 11 is attached to the die pad 12 through the die sealant 13 by a heat treatment. Moreover, a ceramic sealant 16 is applied to top fringes of the die pad 12, and the lead frame 14 is mounted on the die pad 12 through the sealant 16. Also, the ceramic sealant 16 is applied to the lead frame 14, and the upper ceramic plate 15 is fixed onto the leadframe 14 through the sealant 16. Alternatively, the ceramic plate sealant 16 is provided to the lower side of the ceramic upper plate 15, and the ceramic upper plate 15 is mounted onto the lead frame 14. Through a heat treatment, the ceramic plate sealant 16 is molten to seal the lead framed 14 to the ceramic upper plate 15. Additionally, the die 11 and the inner leads of the lead frame 14 are electrically connected by conductive wires 18. The transparent window 10 is sealed by a transparent window sealant 17. For example, the sealant 17 is melted to seal the transparent window 10 to the upper portion of the ceramic upper plate 15 through a heat treatment. Moreover, the lead frame 14 is trimmed, and the fabrication of the package 1 is completed.
The IC package 1 has various weaknesses. For example, the fabrication process for coating the ceramic sealant 16 on the lower side of the ceramic upper plate 15 is complex and costly. Additionally, the desired sealant effect is difficult to achieve between the ceramic upper plate 15 and the window sealant 17. If the window 10 is peeled off from the ceramic upper plate 15, the IC package 1 can be significantly damaged.
FIG. 2 is another conventional IC package with a transparent window. A die 21 is placed on a die pad 22 of a lead frame 23. Lead fingers of the lead frame 23 have electrical connections 25 with the die 21. The die 21 includes an integrated circuit coupled to a light sensor 26. The die 21 and the die pad 22 are covered by a predetermined volume of transparent plastic 24. Thereafter the transparent plastic 24 is molded to form an IC package 2 with a transparent window. The transparent plastic 24 often has an expansion coefficient larger than those of other types of molding compounds. This large expansion coefficient can result in disassociation of the transparent plastic 24 from other components of the IC package 2 after some time of use. For example, the IC package 2 includes a copper die pad, copper leads, and a die surface. The die surface is made of silicon-based material. Such disassociation often leads to cracks and thereby damages the IC package.
Hence it is highly desirable to improve techniques for integrated circuit packaging.